1. Technical Field
This application generally relates to wireless communications, and more particularly to Short Message Service (SMS) messaging and timestamp data associated therewith.
2. Description of the Related Art
Short Messaging Service (SMS) is used to send short messages (i.e. SMS messages) from one mobile station (MS) to another MS, as well as from an External Short Message Entity (ESME) to an MS. An originating MS can use SMS to send an SMS message to a terminating MS that has service from the same or different service provider as the originating MS. SMS messaging protocols may adhere to industry standards, such as the 3rd Generation Partnership Project 2 (3GPP2) specification C.S0015-A. When an originating MS sends an SMS message to another MS, it sends an SMS Teleservice Layer Submit message. When an SMS message is sent from an ESME to an MS, the ESME forwards the SMS message to a Message Center (MC) using a Short Messaging Peer-to-Peer (SMPP) Protocol. The MC of the originating MS processes the SMS submit message. Upon receiving the SMS submit message, the MC of the originating MS creates an SMS Teleservice Layer Deliver message to be sent to the terminating MS. The SMS Teleservice Layer Deliver message includes a Message Center Time Stamp. The Message Center Time Stamp is used by the terminating MS to display the time that the message was sent by the originator.
Some problems exist with implementations of SMS in IS-41-based systems. MCs do not all use the same format for the Message Center Time Stamp subparameter. MCs of some service providers always set the Message Center Time Stamp to Coordinated Universal Time (UTC) time (or Greenwich Mean Time or GMT), regardless of the current or home time zone of the MS. Other service providers set the Message Center Time Stamp to a time that represents the time in the home time zone of the originating MS. An MS can typically be programmed to operate with a given service provider, and typically includes a field in non-volatile memory that indicates if the home MC uses UTC time or home time. An MS uses this field in addition to the Message Center Time Stamp to determine how to appropriately display the time.
If an originating MS associated with an MC using UTC time sends an SMS message to a terminating MS associated with an MC using home time, the terminating MS will not be able to correctly display the time. Likewise, if an originating MS associated with an MC using home time sends an SMS message to a terminating MS associated with an MC using UTC time, the terminating MS will not be able to correctly display the time. Similarly, if an originating MS associated with an MC using home time of a first time zone sends an SMS message to a terminating MS associated with an MC using home time of a different time zone, the terminating MS will not be able to correctly display the time.
If all MSs and MCs could be converted at once using a common and consistent time reference (e.g. UTC time), such problems would be solved. It is not efficient nor practical, however, to simultaneously upgrade the software of millions of previously-deployed MSs. It is also not efficient or practical to simultaneously upgrade the software of all MCs in the network.
Thus, what are needed are methods and apparatus for converting SMS message time stamp information so that terminating mobile stations will always display the correct time. Such techniques need to be introduced in such a way to provide for backwards-compatibility. In conventional systems, the time stamp information is correctly displayed in many instances. For example, when an MS associated with an MC using home time sends an SMS message to another MS associated with an MC using home time in the same time zone, the time stamp information is correctly displayed. With a backwards-compatible solution, appropriate operation occurs when both a prior version MS operates with an upgraded MC and a newer version MS operates with an MC that has not been upgraded.
Cdma2000 also supports a Removable User Identity Module (R-UIM), as described in standard 3GPP2 C.S0023-0 version 4.0. An R-UIM includes a microprocessor and non-volatile memory. The R-UIM stores certain information associated with a user in order to allow a user to easily switch between different Mobile Equipment (ME), and can also be used to store SMS messages. Since it is unaware of the type of time format used by the subscriber's home MC, an ME cannot properly determine how to display the time of the SMS message. Thus, it is further desirable to provide methods and apparatus for consistent SMS message time stamp formatting so that the time of SMS messages stored on an R-UIM can be appropriately displayed when the R-UIM is inserted into different MEs.